1. Field of the Invention
The present invention relates to a piezoelectric pressure sensor suited for detecting a pressure such as a combustion pressure in a cylinder of an internal combustion engine.
2. Description of the Prior Art
The piezoelectric pressure sensor making use of a piezoelectric effect for providing an electricity by applying a stress is widely used in the prior art. Especially, there has been developed a pressure sensor which is suited for detecting the combustion pressure in a cylinder of an internal combustion engine by using a tubular diaphragm. FIG. 1 shows a basic construction of a piezoelectric pressure sensor which is used in the internal combustion engine of the prior art using the tubular diaphragm. FIG. 1 presents a longitudinal section of the sensor which is equipped with a casing having a dual structure. In an inner casing 28, there are disposed a pressure transmission member 29 and a piezoelectric element 27 which are fixed on a base 31 by the fixing force of an upper fixing screw 23. The compression applied to the piezoelectric element 27 by the upper fixing screw is called the "pre-load". This pre-load is essential not only for fixing the piezoelectric element 27 and the pressure transmission member 29 but also for stabilizing the establishment of electricity of the piezoelectric element 27 and for metering the vacuum at a suction stroke of the engine. In the case, however, where the pre-load is applied by the screw, it is difficult to hold the pre-load constant among a plurality of sensors due to dispersions in the surface roughness of screw faces, in the back-lashes of screw portional and in the frictions of screw faces, so that the sensitivities of the individual sensors disperse.